I. Field of the Invention
This invention relates to a recombinant vector which can confer upon potato plants immunity against potato virus Y necrosis line (hereinafter also referred to as "PVY-T"). This invention also relates to a method for conferring immunity against PVY-T upon potato plants and to a potato plant having immunity against PVY-T.
II. Description of Related Art
PVY-T causes tobacco yellow spot necrosis which causes severe necrosis in tobacco. PVY-T is transferred by aphids. If potato plants infected with PVY-T are cultivated, PVY-T may be transferred by aphids, thereby causing severe damage to tobacco. Although PVY-T may cause mosaic disease in potato plants, the symptoms are slight and unclear in a number of varieties, so that it is difficult to remove the diseased plants during cultivation of seed potatoes. Therefore, the diseased potato plants may serve as a source of PVY-T.
With some potato varieties, inoculation of PVY-T causes necrosis spots in the inoculated leaf in the present generation, while in the next generation, symptoms are not observed and infection by PVY-T can not be detected. If these potato varieties are bred by cross breeding, PVY-T-resistant potato plants may be obtained. However, it is expected that it takes as long as 10 years or more to obtain a variety resistant to PVY-T by this method. If resistance to PVY-T can be conferred upon potato plants by genetic engineering techniques, PVY-T-resistant potato plants can be obtained in a short period of time, which is very advantageous.
A method for conferring upon a plant resistance against a virus is known, in which the gene encoding the coat protein (hereinafter also referred to as "CP") of the virus is introduced to the plant (Japanese Laid-open Patent Application (Kokai) Nos. 62-201527 and 62-285791; Plant Cell Technology Vol. 4, No. 2 (1992) pp.101-109, Bio/Technology 8, 127-134 (1990)). According to this method, although resistance against the virus is conferred upon the plant, the plant produces the CP of the virus. If a plant produces a virus CP, amino acids and energy are consumed for the production of virus CP, so that the growth of the plant is not as good as other plants which do not produce the virus CP. Further, in a plant such as potato which is used as a food, the safety of the CP with respect to health must be investigated. Thus, if a plant which is resistant to a virus does not produce the virus CP is obtained, it is very advantageous.